It always bugged me that so little was known about the evolutionary and ecological context of the C. elegans model system. Why haven’t these worms become a model of speciation or ecological adaptation? Compared to Drosophila, evolutionary biologists were slow to take them up. The situation has been getting much better recently, with some really good evo-devo and evolutionary genetics studies coming out in the last few year. Now, this paper should really expand the scope and power of comparative studies:

It describes a field survey of Caenorhabditis population and characterization of lots of new species – their phylogeny, reproductive isolation, phenotypic differences, etc. This should be really exciting for worm people and even, vicariously, for me.

We now have three complete mite genomes. With these plus Daphnia (and more chelicerates, crustaceans, and myriapods on the way), it will be easier to look at the evolution of insect-specific features. Have fun!

As we think about the evolution of enhancers that their role in the evolution of phenotypes, defining the boundaries of the functionally and evolutionarily relevant CREs is one important question (see previous post). Another question/danger/caveat is the potential presence of redundant enhancers contributing to gene expression in the same tissue or organ – the so-called shadow enhancers. In such cases, evolution can modify any or all of these enhancers to change the phenotype. The danger is that any enhancer you identify, even if it is behaving as you expect, may only be telling you part of the story.

In this paper, Scott Barolo, an enhancer-bashing enthusiast and guru, gives a nice overview of shadow enhancers:

After more than 10 years, Michael Ludwig and his colleagues are still squeezing new insights out of the eve stripe 2 enhancer. Here, they show that sequences flanking the experimentally defined minimal enhancer contribute to the fine-tuning and robustness of gene expression. This helps explain Ryan Bickel’s results that we published last year (Composite Effects of Polymorphisms near Multiple Regulatory Elements Create a Major-Effect QTL). Using a population-genetic approach, Ryan showed that the sequence differences responsible for intraspecific phenotypic variation mapped to regions flanking the known functional elements of the bab locus – enhancer, PRE, and promoter – but not inside these regions.

Aside from the pure scientific knowledge it brings, this paper raises interesting practical questions. In our search for well-defined minimal enhancers, where should we stop before we go too far? Evolutionary action may well take place outside of the minimal regions sufficient to drive expression in reporter assays. Striking the right balance between functional characterization and evolutionary relevance may be difficult in some cases.

I cannot say that I agree with it 100%. I myself tend to favor longer sentences, as I feel that some subtlety of meaning and intonation can get lost when a long sentence is cut up. And there should be some room for scientese in science. But there’s no doubt that clarity is the first and foremost duty of a writer. There–I used “but” to start my sentence! Andrew Moore would be proud.